Evolution of the outburst of minor planet (596) Scheila

(596) Scheila was discovered on 1906, Feb. 21 by August Kopff from Heidelberg-Königstuhl Observatory, Germany. It is a “normal” asteroid inside the Main Belt between Mars and Jupiter (a = 2.93 AU, e = 0.17, i = 14.66°), with a diameter around 100Km.
On 2010, Dec. 11, Steve Larson of the Catalina Sky Survey discovered a coma around it, and it was soon followed by other observers, including us.
Archived Catalina images suggest that this outburst may have started around December 3, 2010, when Scheila appeared a little brighter than expected but with no obvious coma.
Just only for this activity, Scheila became a member of the Main-Belt Comets.
Here are our first image of the object, taken the day after the discovery of the coma:

The “cloud” of dust is clearly visible, also on images taken after two days, on 2010, December 14:

Our last image was taken on 2011, Jan. 02.18:

The coma is only barely visible as a sort of faint cloud around the asteroid. The outburst is definitely finished.

CBET 2632, issued on 2011 Jan. 12, reports, among other things, about spectroscopic observations of (596) Scheila obtained with FORS2 attached to one of the VLT by astronomers from Liege University. Spectra does not show any extended cometary gaseous emissions, but only a spatially extended continuum due to dust-scattered sunlight.
Those preliminary results are in favor of a collisional scenario to explain the outburst of (596) Scheila, rather than a cometary driven activity.

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